Generally, as for a method for forming various thin films made of a dielectric material, a metal, a semiconductor or the like, there is known a CVD (chemical vapor deposition) method for forming a film by supplying an organic material gas such as an organic metal compound or the like to a film forming chamber and causing a reaction between the organic material gas and another gas such as oxygen, ammonia or the like. An organic material used in the CVD method often exists in a liquid or a solid state at a room temperature, so that a vaporizer for vaporizing the organic material is required. The organic material becomes a liquid source material by, e.g., dilution or dissolution using a solvent.
The liquid source material is vaporized to a source gas while being sprayed into a heated vaporization chamber along with, e.g., a carrier gas flow, through a spray nozzle provided at the vaporizer. The source gas is supplied to the film forming chamber and reacts with another gas therein, so that a predetermined film is formed on a substrate (see e.g., Japanese Patent Laid-open Publication Nos. 2000-58528, 2005-109349, H3-126872, H6-310444 and H7-094426).
A flow rate of the source gas required in the vaporizer varies depending on types of liquid source materials or types of processing using the source gas, such as film formation and the like. Accordingly, conventionally, there is provided a vaporizer in which a discharge port of the spray nozzle, a size of a carrier gas flow path or the like are designed so as to maximize vaporization efficiency of the liquid source material in accordance with a flow rate of the source gas required by the vaporizer. Therefore, in the conventional case, the change in types of processing using the source gas demands replacement of the entire vaporizer with another vaporizer capable of coping with a flow rate of the source gas required for the processing.
However, if the entire vaporizer is replaced whenever the types of processing are changed, there arises a need to design a vaporizer which can cope with a flow rate of the source gas required for the processing and examine reliability of the vaporizer. As a result, manufacturing throughput decreases, and a development cost of a vaporizer increases. Further, since, for example, it is required to manage various vaporizers in accordance with various flow rates of the source gas, the management of the vaporizers becomes complicated.
Moreover, in the case of the above-described vaporizer which generates a source gas by vaporizing a liquid source material ejected from a spray nozzle, it is required to eject small-sized liquid droplets obtained by minimizing the discharge port of the spray nozzle in view of vaporization efficiency.
If the discharge port of the spray nozzle is minimized, in order to increase a flow rate of the source gas, it is considered to increase, e.g., a flow rate of a carrier gas. Since, however, the increase in a flow rate of the carrier gas is limited, it is unavoidable to increase the discharge port of the spray nozzle in order to further increase a flow rate of the source gas. This results in an increase in a size of the liquid droplets of the liquid source material ejected from the spray nozzle, so that the vaporization efficiency is lowered. As such, in the conventional vaporizer, it is considerably difficult to increase a flow rate of the source gas while maintaining vaporization efficiency.